Electrode-cathode



Au 27,1940. G. s. EVANS 7 2,2 ,8

ELECTRODE-CATHODE (REPLENISHING COATING) Filed Oct. 19, 1938 E M m: a

ATTORNEY Patented Aug. 27, 1940 ELECTRODE-GATHODE- (REPLENISIQIING COATING) George Stark Evans, East Orange, N. J., assignor to Westinghouse Electric '85 Manufacturing 7 Company, East Pittsb of Pennsylvania Application October 19, 1938, Serial No. 235,707

urgh, Pa., .'a corporation 2 Claims. (01. 250-275) My invention relates to gaseous discharge devices and especially to such devices utilized with high currentvalues. w

. An object of my invention is to provide acathode in a discharge device that is capable of withstanding severe overloads. Otherobjects and advantages of my invention will be. apparent from the following description :and drawing, in which: Fig, ,1 is aview in front elevation of a tube with'a portion of the container broken away to disclose the anode in elevation and the cathode partlyinjelevation and partly in cross-section.

2 islan enlarged view on lines II.II .of Fig. 1.

Fig.- 3 is,a modification of the cathode structure of Fig. 1.

Fig. 4 is an enlarged view on lines IV-IV of Fi 3.

Discharge devices of the rectifier and gridcontrolled discharge type, either commonly employ an oxide coated base metal which is either directly or indirectly heated, or utilize a mercury vapor pool. The mercury vapor pool pro- 25 vides a problem in coveniently and constantly starting the discharge when desired, but the pool type is capable of standing high currents.

The oxide coated cathode, on the other hand, has'a property of starting the discharge easily go when desired, but has the difiiculty that, at

overloads, the cathode is apt to have its oxide coating stripped from the base metal with some violence and rendered useless or practically so.

It is an object of my invention to provide a 5 cathode capable of higher current ratings and capable of withstanding severe overloads.

In particular, the cathode structure of my invention has the properties of the mercury pool cathode of withstanding high values of discharge current by its function of acting as a reservoir for an electron emitting material of a low-work function metal such as the alkaline earth metals and especially barium. The use of the alkaline earth material retains the sensitive initiation of 45 the discharge common to the oxide coated cathode.

A preferred embodiment of the invention is illustrated in the drawing. The container It may be of glass to provide an enclosure for the 50 discharge space. Of course, other types of containers may be used, including those of metal with insulated lead-in seals for certain of the electrode or electrodes. Inside of the container is the anode II which may be of any suitable 55 form and shape such as that disclosed. The

cathode structure comprises a liquid portion" [2 and a metal portion to be describedjlat'en' 'The liquid l2 comprises mercury containing a percentage of alkaline earth material and the alkaline earth material that-I'preferto'usefis that bodiment illustrated, Iprefer to'limit-the' barium toa:va1ue 'at which themalgam retains its liquid form.- Even a small 'percentage ofbariumsuch aslone-tenth of a percent may be used and I have obtained advantageous results with threetenths .of a percent .of barium in the mercury p001. I, The metal Fig. l, a coil .of wireczl3having-one-ofits ends dipping into theliquid portion of the cathode. The lower end of this coil is connected to the cathode lead-in wire l4 through the bottom portion of the container and the upper end of the coil is connected to another lead-in wire i5 that may leavethe tube at any desired portion, such as the top part of the tube as illustrated. I prefer to surround the coil l3 with a hollow tubular member [6 which is partly immersed in the liquid portion of the cathode and connected to the lead-in wire M by a connecting support I1.

In operation, a heating current is passed through the coil l3 and the heat from this coil vaporizes the adjacent surface of the mercury. The barium or'other alkaline earth metal may evaporate from the amalgam and deposit on the metal cathode surface and emit electrons therefrom. Barium may also migrate from the amalgam to the base metal cathode surfacebecause of the contact between the two. Certain mercurides of barium are formed in the amalgam and may be mechanically carried by the mercury vapor. These mercurides when contacting with the cathode base metal, decompose and leave a barium deposit. Barium metal may also be mechanically carried by the mercury. vapor to be deposited on the cathode base metal. Barium may also be liberated from the amalgam and ionized by the discharge in the tube with the result that the barium ions return to the cathode to activate the base metal. The mechanism of getting barium from the amalgam reservoir to the metal cathode surface may be any one or a combination of the above possible'ways. Once barium is on a cathode and the cathode is heated, thencopious emission of the electrons may be obtained. The barium on the cathode is also being continually replenished. An overload may normally deplete the cathode of its barium, but

portion 'of the cathode comprises in an instant later, barium will be deposited on the cathode metal and the cathode will continue to operate as long as the base metal itself is in operable condition.

The coil l3 in the figure is preferably of tungsten, although molybdenum or other refractory material may be used, and is surrounded by one or more refractoryradiation shields l6 preferably of molybdenum. The tubular member IE not only acts as a radiation shield, but also directs the'barium laden vapors from the pool to the hot emitting surfaces of the cathode. If the innermost radiation shield is positioned close enough to the coil so that the heat from the coil and the discharge heats it to an emitting temperature, then the discharge between the anode and the cathode may start from either the coil or the radiation shield connected thereto. The discharge device constructed as disclosed in the drawing is simple in construction, easy to, out-gas, and has withstood overloads that would irreparably destroy an'oxide coated cathode of the same wattage in-put. I prefer to keep the amalgam in aliquid state so that there will always be plenty of. mercury condensed on the walls of the container to wash particles of barium back to the liquid cathode.

Many modifications may be made in the form, arrangement, and number of the elements disclosed in the preferred embodiment. One such modification, namely, an indirectly heated cathode surface is illustrated in Figs. 3 and 4 in which the heater wire is enclosed .in a tubular metal member 2|, partly immersed in the liquid cathode 22. The tubular member 2| has projecting vanes 23 therefrom to provide a greater cathode surface. Some of these vanes may also support a tubular shield 24 similar in purpose to the protecting tube l6 of Fig. 1. In this construction, a. more delicate heating wire 20 of any suitable conducting material may be used because it is protected from the discharge by the metal tube 2| and its closure members 25 and 26. The material of the tube 2|, vanes 23, and protective tube 24 may be of molybdenum or other material that is capable of withstanding the heat generated by a heavy discharge current. The shape of the coil and shield or shields, may be considerably varied from the ones disclosed in the various figures of the drawing.

Still further modifications may be made without departing from the spirit of the invention.

I claim:

1. A discharge device comprising a container having an alkaline earth liquid amalgam, an anode within said container, a cathode metallic surface partly immersed in said amalgam and directly exposed at said immersion to the discharge path toward said anode, a heater coil adjacent the surface of said amalgam and metallic surface, and cathode connections having a conductive path to said heater coil and metallic surface.

2. A discharge device comprising a container, an anode therein, an alkaline earth liquid amalgam within said container, a metal tube having one end immersed in said amalgam, a heater coil within said tube adjoining the surface of said liquid amalgam, and cathode connections having a conductive path to both said metal tube and said. heater coil, said metal tube being the cathode 

